1. Field of the Invention
The present invention relates to a wire drawing composite die having excellent properties and a process for the production of the same. More particularly, it is concerned with a wire drawing diamond compact comprising a diamond compact bonded coherently to a cerment containing molybdenum and a process for the production of the same.
2. Description of the Prior Art
As a composite polycrystalline diamond die for wire drawing, there has been proposed such a structure that the circumference of a diamond compact using cobalt as a binder is surrounded by a cemented carbide alloy of WC-Co (Japanese Patent Application (OPI) No. 26746/1975) and this diamond die has been marketed. In a wire drawing die using this diamond compact, a surrounding support consisting of a WC-Co alloy is subjected to grinding and forcibly put in a high strength binding ring, whereby the diamond compact part is pressurized, and this diamond die is more suitable for drawing a wire rod which is hard to break and has a high strength than the prior art single crystal diamond die.
The inventors have traced Examples disclosed in the above described patent publication, but, for all practical purposes, it is considerably difficult to use the WC-Co green compact as disclosed therein. The reason is that it is difficult to take measures to cope with the situation that the WC-Co green compact contains a large quantity of gaseous components because of being finely powdered and it is difficult to hold the shape thereof during hot pressing because of a low strength.
The inventors have made studies on the use of a sintered body of WC-Co alloy as a support for a diamond compact and, consequently, have dissolved the above described two problems. In this case, however, there occurs a new problem that the sintered body of WC-Co alloy tends to be cracked. This is due to that the sintered body of WC-Co is subject to a stress of higher than the strength thereof during hot pressing and since ordinarily, the pressure is firstly raised to a desired pressure followed by raising the temperature, the WC-Co body cannot be adapted to a deformation of a pressed part during raising of the pressure.
When a commercially sold polycrystalline diamond die using a WC-Co alloy as a surrounding support is really used in the field where natural diamond dies are used, it is found that there are various problems. That is, these problems are that the surface of a drawn wire rod is often scratched stripewise, seizure sometimes takes place and the diameter of a wire varies, in particular, when using a soft material, because the drawing force of the former diamond die is larger than that of the natural diamond die.
The above described diamond compact commercially sold for dies is a sintered body of diamond particles of about 60 microns, which contains a binder phase consisting predominantly of cobalt in a proportion of about 10% by volume. The foregoing publication describes that the liquid phase of the eutectic composition of a WC-Co alloy as a support enters diamond particles from the circumference during sintering to thus form a binder phase. When the inside of a die causing troubles is observed, it is found that a drawn material is deposited on the binder phase and the diamond particles partly fall off with the binder phase.